Twin Studies of Behavior

Abstract

In the age of molecular genetics some commentators have questioned whether twin studies will continue to be a useful tool for studying genetic influences on behavior. Many of us think the answer is yes (Bouchard & Propping, 1993). Work with monozygotic twins reared apart provides an imperfect, but nevertheless powerful window on the direct influence of genes on whole organisms. Extended behavior genetics designs that include twins also provide important information about more complex modes of inheritance that will be very difficult to implement with molecular techniques (Lykken, McGue, Tellegen, & Bouchard, 1992). In this presentation I will attempt to illustrate these points and bring you up-to-date on new findings and new twists on old findings in the field of behavior genetics. In order to illustrate the breath and implications of these findings, first, I will sample the major human individual differences—psychological interests, mental abilities, personality, social attitudes and psychopathology—and illustrate the breath and magnitude of genetic influence in each of these domains. Secondly, I will illustrate the much less well-known fact that measures of the environment that are often purported to be “causal agents” may also be a manifestation of genetic influences rather than causal agents in their own right.

Burks, B. S. (1938). On the relative contributions of nature and nurture to average group differences in intelligence. Proceedings of the National Academy of Sciences, 24, 276–282.CrossRefGoogle Scholar

Freeman, F. N., Holzinger, K. J., & Mitchell, B. C. (1928). The influence of environment on the intelligence, school achievement and conduct of foster children. In G. M. Whipple (Eds.), Nature and nurture: Their influence on intelligence (The 27th yearbook of the National Society for the Study of Education, Pt. 1) Bloomington, Ill: Public School Publishing.Google Scholar